65 research outputs found
Recommended from our members
New neutron cross section and fission yield data for SNManalysis
Neutron cross-section data are fundamental for the design ofnuclear interrogation systems, the maintenance of nuclear materials andwaste, and the understanding the consequences of nuclear catastrophe.Although a large body of nuclear data exists, it is often old,unreliable, or poorly determined. For several years we have collaborated,as part of an IAEA Coordinated Research Project, to precisely measure thepartial thermal neutron gamma ray cross sections for all elements fromhydrogen to uranium at the Budapest Reactor. These data will replace theunreliable tables of Lone et al [1], still widely in use, and will bepublished as an IAEA TECDOC
Recommended from our members
Prompt gamma activation analysis (PGAA) and short-lived neutron activation analysis (NAA) applied to the characterization of legacy materials
Without quality historical records that provide the composition of legacy materials, the elemental and/or chemical characterization of such materials requires a manual analytical strategy that may expose the analyst to unknown toxicological hazards. In addition, much of the existing legacy inventory also incorporates radioactivity, and, although radiological composition may be determined by various nuclear-analytical methods, most importantly, gamma-spectroscopy, current methods of chemical characterization still require direct sample manipulation, thereby presenting special problems with broad implications for both the analyst and the environment. Alternately, prompt gamma activation analysis (PGAA) provides a'single-shot' in-situ, non-destructive method that provides a complete assay of all major entrained elemental constituents.1-3. Additionally, neutron activation analysis (NAA) using short-lived activation products complements PGAA and is especially useful when NAA activation surpasses the PGAA in elemental sensitivity
Recommended from our members
Neutron-induced prompt gamma activation analysis (PGAA) of metalsand non-metals in ocean floor geothermal vent-generated samples
Neutron-induced prompt gamma activation analysis (PGAA) hasbeen used to analyze ocean floor geothermal vent-generated samples thatare composed of mixed metal sulfides, silicates, and aluminosilicates.The modern application of the PGAA technique is discussed, and elementalanalytical results are given for 25 elements observed in the samples. Theelemental analysis of the samples is consistent with the expectedmineralogical compositions, and very consistent results are obtained forcomparable samples. Special sensitivity to trace quantities of hydrogen,boron, cadmium, dysprosium, gadolinium, and samarium isdiscussed
Designing a broad-spectrum integrative approach for cancer prevention and treatment
Targeted therapies and the consequent adoption of "personalized" oncology have achieved notablesuccesses in some cancers; however, significant problems remain with this approach. Many targetedtherapies are highly toxic, costs are extremely high, and most patients experience relapse after a fewdisease-free months. Relapses arise from genetic heterogeneity in tumors, which harbor therapy-resistantimmortalized cells that have adopted alternate and compensatory pathways (i.e., pathways that are notreliant upon the same mechanisms as those which have been targeted). To address these limitations, aninternational task force of 180 scientists was assembled to explore the concept of a low-toxicity "broad-spectrum" therapeutic approach that could simultaneously target many key pathways and mechanisms. Using cancer hallmark phenotypes and the tumor microenvironment to account for the various aspectsof relevant cancer biology, interdisciplinary teams reviewed each hallmark area and nominated a widerange of high-priority targets (74 in total) that could be modified to improve patient outcomes. For thesetargets, corresponding low-toxicity therapeutic approaches were then suggested, many of which werephytochemicals. Proposed actions on each target and all of the approaches were further reviewed forknown effects on other hallmark areas and the tumor microenvironment. Potential contrary or procar-cinogenic effects were found for 3.9% of the relationships between targets and hallmarks, and mixedevidence of complementary and contrary relationships was found for 7.1%. Approximately 67% of therelationships revealed potentially complementary effects, and the remainder had no known relationship. Among the approaches, 1.1% had contrary, 2.8% had mixed and 62.1% had complementary relationships. These results suggest that a broad-spectrum approach should be feasible from a safety standpoint. Thisnovel approach has potential to be relatively inexpensive, it should help us address stages and types ofcancer that lack conventional treatment, and it may reduce relapse risks. A proposed agenda for futureresearch is offered
Recommended from our members
New capture Gamma-Ray library and Atlas of spectra for all elements
A new library comprising 30 thousand neutron capture gamma rays has been created by combining new measurements on natural elements from Budapest and literature data for all stable isotope targets. All energies and intensities are consistent in that they are based on the chlorine and nitrogen standards, respectively. Accurate neutron binding energies and thermal capture cross-sections could also be inferred for all cases where the level scheme is sufficientlycomplete. The new data can be used for nuclear structure investigations, reaction model calculations, and a number of applications, such as Prompt Gamma-ray Activation Analysis (PGAA)
Recommended from our members
New capture Gamma-Ray library and Atlas of spectra for all elements
A new library comprising 30 thousand neutron capture gamma rays has been created by combining new measurements on natural elements from Budapest and literature data for all stable isotope targets. All energies and intensities are consistent in that they are based on the chlorine and nitrogen standards, respectively. Accurate neutron binding energies and thermal capture cross-sections could also be inferred for all cases where the level scheme is sufficientlycomplete. The new data can be used for nuclear structure investigations, reaction model calculations, and a number of applications, such as Prompt Gamma-ray Activation Analysis (PGAA)
Recommended from our members
New catalog of neutron capture gamma rays for prompt gamma activation analysis
Thermal neutron capture gamma rays were measured for all stable elements at the guided neutron beam facility in Budapest. Energies, relative intensities, and partial production cross-sections were determined with high precision for about 14,000 gamma rays of 82 elements. The new experimental data were supplemented with isotopic data from ENSDF and the original papers and were evaluated. The resulting accurate new levels and decay schemes comprise 35,000 gamma-ray transitions. The new database is practically complete for light nuclei, hence capture cross sections could be inferred from the measured partial gamma-ray production cross-sections. Precise neutron separation energies were also deduced from fits to the level schemes. The new elemental datasets will be the basic input to an IAEA database for prompt gamma activation analysis, a chemical method of elemental analysis. The new isotopic sets will be provided for updating the thermal neutron capture datasets of ENSDF
Recommended from our members
A new prompt gamma-ray database for cold and thermal neutron capture
Comprehensive prompt neutron capture gamma-ray data are important for basic nuclear structure studies, reaction mechanisms, sorr-process nucleosynthesis, and applications like Prompt Gamma Ray Activation Analysis (PGAA). The only readily available prompt neutron capture gamma ray library is the compilation by Lone et al1. These data are elemental measurements without anyisotopic assignments reported. They were measured with early, small Ge(Li) detectors and have numerous contaminant peaks, missing transitions, and limited uncertainty information. The Evaluated Nuclear Structure Data File (ENSDF)2 has more up-to-date information and is organized by isotope. The ENSDF neutron capture intensities are not normalized to absolute cross sections, but instead to per 100 decays of the parent. These normalizations are seldom more precise than +-10% and are not useful for applications like PGAA. Until now no completely satisfactory library of prompt neutron gamma rays has been produced. New prompt gamma-ray data have emerged from a series of experiments at the 10-MW Budapest Research Reactor. Accurate gamma-ray energies and production cross sections have been measured for nearly all elements from hydrogen to uranium. The measurements were performed with natural targets using a subthermal guided neutron beam and a Compton-suppressed HPGespectrometer. Energies were measured with respect to well-known 35Cl neutron-capture gamma rays. Gamma-ray production cross sections were determined with respect to the 1H capture cross section using internal standards, mostly stoichiometric compounds, to avoid corrections for neutron absorption and scattering. Precision of a few percent was attained for the strongest gamma rays from most elements. The Budapest data is precise, but the complexity of elemental measurements often makes it difficult to resolve weak transitions. To remedy this situation we are combining the isotopic data from ENSDF with the Budapest elemental data as part of an International Atomic Energy Agency Coordinated Research Project. The ENSDF file often contains precise energies and relative transition intensities that were measured with separated isotope targets. We are using ENSDF to assign the gamma rays in the Budapest datasets to the correct isotopes and place them in the level scheme. The level energies are then least-squares fit to the gamma-ray energies todetermine the self-consistency of the data. Outliers are a possible indication of unrecognized multiplets or errors in the level schemes. The ENSDF gamma-ray intensities are then renormalized to the identical scale as the Budapest intensities. The two datasets are then averaged and discrepancies are noted and corrected. The resulting prompt gamma-ray neutron capture database will be more completeand self-consistent then either of the component databases. In special cases additional corrections for non-unity Westcott g-factors will be provided.A first pass through the Budapest data has been completed, and we have assigned gamma rays for each element to the level schemefor the appropriate isotope based on ENSDF. This provides a database for identifying impurities in the spectra. We have also compared the observed cross section yields, based on the level scheme or the decay gamma rays, with those compiled by Mughabghabet al3. Although our values should be less than or equal to the compiled values, depending on the completeness of the level scheme, we found that many values differed well beyond the error bars. The final analysis of the prompt gamma-ray neutron capture database is in progress and we will report on our results in this paper in this presentation
Recommended from our members
Determination of contamination in rare earth materials by prompt gamma activation analysis (PGAA)
Prompt gamma activation analysis (PGAA) has been used to detect and quantify impurities in the analyses of rare earth (RE) oxides. The analytical results are discussed with respect to the importance of having a thorough identification and understanding of contaminant elements in these compounds regarding the function of the materials in their various applications. Also, the importance of using PGAA to analyze materials in support of other physico-chemical studies of the materials is discussed, including the study of extremely low concentrations of ions such as the rare earth ions themselves in bulk material matrices
- …